1. Field of the Invention
The present invention relates to systems and methods for protecting vehicle occupants from injury. More specifically, the present invention relates to devices that intelligently control gas venting from an inflatable cushion to enhance the protection provided by the cushion.
2. Description of Related Art
The inclusion of inflatable safety restraint devices, or airbags, is now a legal requirement for many new vehicles. Airbags are typically installed in the steering wheel and in the dashboard on the passenger side of a car. Additionally, airbags may be installed to inflate beside the passenger to provide side impact protection, in front of the knees to protect the knees from impact, over a passenger's head, or at other strategic locations.
In the event of an accident, an accelerometer within the vehicle measures the abnormal deceleration and triggers the ignition of a pyrotechnic charge. Expanding gases from the charge fill the airbags, which immediately inflate to protect the driver and/or passengers from impact against the interior surfaces of the vehicle. During normal vehicle operation, airbags are typically stowed behind covers to protect them from tampering and provide a more attractive interior facade for the vehicle.
Some airbag cushions have vents that are designed to permit inflation gas to escape from the cushion at a measured rate, thereby providing a softer cushion. Softer cushions are beneficial in low velocity collisions, in which the cushion need not be extremely stiff to prevent the occupant from contacting the vehicle interior. However, for high speed collisions, a stiffer cushion is needed to more rapidly absorb the occupant's velocity; hence, comparatively less venting is desirable. Other factors, such as the occupant's weight and position influence the optimal stiffness of the cushion.
Since all of the above factors can be expected to vary for any single vehicle, it would be desirable to create a system capable of varying the cushion stiffness in response to changes in vehicle velocity, occupant weight, occupant position, and the like. The desirability of such a system is reflected in the United States government's new frontal safety requirements, as set forth in the FMVSS 208 Ruling.
In response to such a need, some airbag systems have been designed with variable venting systems. Such variable venting systems typically have one or more vents formed in the rigid module housing; the vents are covered or uncovered through the use of some type of actuation mechanism. Thus, the amount of venting that occurs through the rigid module housing can be controlled to influence the stiffness of the cushion.
Unfortunately, known variable venting systems are limited in many respects. For example, many such systems utilize an actuation mechanism that is too slow to reliably permit the desired degree of venting to occur prior to impact of the occupant against the cushion. Some variable venting systems are simply too slow to vary the cushion stiffness based upon the impact velocity, and are thus unable to adapt the stiffness of the cushion to suit the severity of the collision.
Additionally, placement of vents on the rigid module housing imposes limitations on the size, shape, and location of the vents. Thus, the optimal degree of venting may be unobtainable. More precisely, the vents may not be large enough to release enough gas to soften the cushion as much as may be desirable. The vents may also be obstructed by internal components of the vehicle, thereby further reducing the degree of cushion adaptation that can be achieved.
Furthermore, many known variable venting systems are somewhat complex and expensive to produce. Often, several custom-manufactured parts are required. The design of the airbag module may be unduly hindered by placement of the vents on the rigid module housing; such placement may interfere with the positioning of other module components such as the inflator, mounting hardware, and the like.
Accordingly, a need exists for an airbag module and associated manufacturing and activation methods by which the stiffness of the cushion can be rapidly adapted. Preferably, such adaptation occurs rapidly enough to take effect after the collision, and yet before the occupant strikes the cushion. Furthermore, such an apparatus and method preferably provides a sufficiently wide variation in cushion stiffness to perform well under high as well as low velocity impact conditions. Yet further, such an apparatus and method is preferably inexpensive and simple to manufacture, with a minimum of modification to existing airbag module designs.